Neutron Sources for Materials Research T E Mason

Neutron Sources for Materials Research T. E. Mason Experimental Facilities Division Spallation Neutron Source Acknowledgements: Jack Carpenter X 0000910/arb SNS Experimental Facilities Oak Ridge

Neutrons and Neutron Sources • The neutron was discovered in 1932 by Chadwick • Coherent neutron diffraction (Bragg scattering by crystal lattice • planes) was first demonstrated in 1936 by Mitchel & Powers and Halban & Preiswerk as an exercise in wave mechanics The possibility of using the scattering of neutrons as a probe of materials developed with the availability of copious quantities of slow neutrons from reactors after 1945. Fermi's group used Bragg scattering to measure nuclear cross-sections X 0000910/arb 98 -6245 uc/vlb SNS Experimental Facilities 2 Oak Ridge

Neutrons and Neutron Sources • A reactor moderates the neutrons produced in the fission chain reaction resulting in a Maxwellian energy distribution peaked at T (300 K). X 0000910/arb 98 -6243 uc/rfg SNS Experimental Facilities 3 Oak Ridge

Neutrons and Neutron Sources • The application of slow neutron scattering to the study of condensed matter had its birth in the work of Wollan and Shull (1948) on neutron powder diffraction: • The neutron is a weakly interacting, non-perturbing probe with • simple, well-understood coupling to atoms and spins The scattering experiment tells you about the sample not the probe X 0000910/arb 98 -6244 uc/rfg SNS Experimental Facilities 4 Oak Ridge

Neutrons and Neutron Sources • You can easily work in extreme sample environments H, T, P, . . . ) • e. g. 4 He cryostat (Shull & Wollan) and penetrate into dense samples The magnetic and nuclear cross-sections are comparable, nuclear cross-sections are similar across the periodic table • Sensitivity to a wide a range of properties, both magnetic and structural SNS Experimental Facilities X 0000910/arb 98 -6242 uc/rfg 5 Oak Ridge

Neutrons and Neutron Sources • Energies and wavelengths of thermal and cold neutrons are well matched to relevant energy scales in condensed matter (300 K = 30 me. V, 50 K = 5 me. V) – Inelastic experiments with good energy (1 me. V) and momentum (0. 01 Å-1) are possible • Cross-section is proportional to static and dynamic correlation functions – Results are of direct relevance to modern mathematical descriptions of interacting systems - Superconductivity Magnetism Phase transitions Electronic properties Non-equilibrium phenomena Structure and dynamics X 0000910/arb 98 -6246 uc/vlb SNS Experimental Facilities 6 Oak Ridge

Neutrons and Neutron Sources • Work leading to the development of inelastic neutron • scattering was carried out throughout the 50's The real breakthrough was the development of the “constant-Q” mode of operating the triple-axis spectrometer pioneered by Brockhouse and co-workers at Chalk River: – this permitted the systematic investigation of the dynamic response of the material – concentrating on the regions of interest X 0000910/arb 98 -6241 uc/rra SNS Experimental Facilities 7 Oak Ridge

How Are Neutron Beams Produced? • Neutrons are one of the fundamental building blocks of matter that can be released through: – The fission process by splitting atoms in a nuclear reactor – The spallation process by bombarding heavy metal atoms with energetic protons • The moderated neutrons, once released, can be transmitted through beam guides into the laboratory and used for a wide variety of research and development projects SNS Experimental Facilities 8 X 0000910/arb 98 -3807 A uc/djr Oak Ridge

Development of Neutron Science Facilities X 0000910/arb 97 -3924 E uc/djr SNS Experimental Facilities 9 Oak Ridge

Neutrons: Where? • Fission: n + 235 U = n + fragments Sustain chain reaction moderated by 200 Me. V/n available D 2 O (H 2 O) to E = T (Maxwellian) X 0000910/arb 98 -6239 uc/vlb SNS Experimental Facilities 10 Oak Ridge

Types of Neutron Sources • Reactor e. g. , ILL, France ~1. 5 x 1015 n/cm 2/s (recently underwent major refurbishment) Advantages: – high time averaged flux – mature technology (source + instruments) – very good for cold neutrons Drawbacks: – licensing (cost/politics) – no time structure X 0000910/arb 98 -6237 uc/rra SNS Experimental Facilities 11 Oak Ridge

The Institut Laue-Langevin, Grenoble X 0000910/arb 2000 -05269 uc/arb SNS Experimental Facilities 12 Oak Ridge

Types of Neutron Sources • Pulsed reactor – – only tried in Russia - IBR II Dubna 2 Hz 1500 MW when on Advantages: – high peak flux Drawbacks: – time structure not optimal (low average) – unlicenseable in the west X 0000910/arb 98 -6238 uc/rra SNS Experimental Facilities 13 Oak Ridge

Schematic View of the IBR-2, Dubna X 0000910/arb 2000 -05274 uc/arb SNS Experimental Facilities 14 Oak Ridge

The Principal Characteristics of the IBR-2 Reactor X 0000910/arb 2000 -05276 uc/arb SNS Experimental Facilities 15 Oak Ridge

Schematic Layout of the IBR-2 Experimental Hall 1 -DIFRAN 2 -DIN-2 PI 3 -RR 4 -Yu. MO 5 -HRFD 6 a-DN-2 6 b-SNIM-2 7 a-NSVR 7 b-NERA-PR 8 -SPN 9 -REFLEX 10 -KDSOG-M 11 -ISOMER 12 -DN-12 13, 14 -test channels X 0000910/arb 2000 -05275 uc/arb SNS Experimental Facilities 16 Oak Ridge

Neutrons: Where? • Spallation: p + heavy nucleus = 20 n + fragments 1 Ge. V e. g. W, Pb, U 23 Me. V/n flux DR 3 ILL Risø Grenoble ~2 x 1014 n/cm 2/s ~1. 5 x 1015 n/cm 2/s ISIS average 2 x 1013 n/cm 2/s 8 x 1015 n/cm 2/s X 0000910/arb 98 -6240 uc/vlb SNS Experimental Facilities 17 Oak Ridge

Spallation-Evaporation Production of Neutrons Original Nucleus Recoiling particles remaining in nucleus ‘ ‘ ‘ Ep Emerging “Cascade” Particles ~ (high energy, E < Ep) (n, p. π, …) (These may collide with other nuclei with effects similar to that of the original proton collision. ) ‘ Proton ‘ Excited Nucleus ‘ ‘ g ‘ Residual Radioactive Nucleus > ~ 1 sec ‘ Evaporating Particles (Low energy, E ~ 1– 10 Me. V); (n, p, d, t, … (mostly n) and g rays and electrons. ) ‘ ~10– 20 sec e g g Electrons (usually e+) and gamma rays due to radioactive decay. ‘ e X 0000910/arb SNS Experimental Facilities 18 Oak Ridge

Types of Neutron Sources • Pulsed spallation source e. g. , ISIS, LANSCE 200 µA, 0. 8 Ge. V, 160 k. W 2 x 1013 n/cm 2/s average flux 8 x 1015 n/cm 2/s peak flux Advantages: – high peak flux – advantageous time structure for many applications – accelerator based – politics simpler than reactors – technology rapidly evolving Disadvantages: – low time averaged flux – not all applications exploit time structure – rapidly evolving technology X 0000910/arb 98 -6235 uc/rra SNS Experimental Facilities 19 Oak Ridge

IPNS Facilities Map X 0000910/arb 2000 -05272 uc/arb SNS Experimental Facilities 20 Oak Ridge

ISIS Instruments X 0000910/arb 2000 -05273 uc/arb SNS Experimental Facilities 21 Oak Ridge

Types of Neutron Sources • CW spallation source e. g. , PSI 0. 85 m. A, 590 Me. V, 0. 9 MW 1 x 1014 n/cm 2/s average flux Advantages: – high time averaged flux – uses reactor type instrumentation (mature technology) Disadvantages: – no time structure – high background X 0000910/arb 98 -6236 uc/rra SNS Experimental Facilities 22 Oak Ridge

PSI Proton Accelerators and Experimental Facilities X 0000910/arb 2000 -05270 uc/arb SNS Experimental Facilities 23 Oak Ridge

Principle of the Spallation Neutron Source SINQ X 0000910/arb 2000 -05271 uc/arb SNS Experimental Facilities 24 Oak Ridge

The Materials Testing Accelerator • E. O. Lawrence conceived this project in the late 1940 s as a means to produce Pu-239 and tritium, and later, U-233. Despite its name, MTA was never intended for materials research. Work went on at the site of the present Lawrence Livermore Laboratory, where scientists accomplished substantial high power accelerator developments. Efforts continued until 1955 when an intense exploration effort revealed large Uranium ore reserves in the U. S. and the project terminated. By that time the pre-accelerator had delivered CW proton currents of 100 m. A and 30 m. A of deuterons. The work was declassified in 1957. X 0000910/arb 2000 -05265 uc/arb SNS Experimental Facilities 25 Oak Ridge

The Materials Testing Accelerator: Machine Parameters • There was already by that time some information on the production of spallation neutrons by 190 -Me. V deuteron-induced spallation on Uranium, about 30% more than by protons of the same energy. This guided the choice of accelerated particle type and beam energy. With the anticipated required production rate, the parameters of the accelerator were set: – Deuterons – Particle energy – 500 Me. V – CW operation – 320 m. A (beam power 160 MW) X 0000910/arb 2000 -05266 uc/arb SNS Experimental Facilities 26 Oak Ridge

The Materials Testing Accelerator: Target • Original ideas concerned a Uranium target • Subsequent development led to target systems alternatives • including moderated subcritical lattices (k < 0. 9) Finally the chosen target system consisted of a Na. K-cooled Beryllium primary target, and depleted Uranium secondary target for neutron multiplication, within a water-cooled depleted Uranium lattice for breeding Plutonium X 0000910/arb 2000 -05267 uc/arb SNS Experimental Facilities 27 Oak Ridge

Sketch of Cutaway View of Linear Accelerator – Looking East – Injector End X 0000910/arb 2000 -05268 uc/arb SNS Experimental Facilities 28 Oak Ridge

The ING Project • The Chalk River Laboratory of Atomic Energy of Canada • Limited launched the Intense Neutron Generator (ING) Project in 1964. The goal was a “versatile machine” providing a high neutron flux for isotope production and neutron beam experiments. Work continued until late 1968 when the project was cancelled due to the perceived high costs and insufficient political support in the Canadian scientific community. ING was estimated to cost about $150 M to build and about $20 M/yr to operate. Technical developments that resulted from the ING project were significant, even seminal X 0000910/arb 2000 -05257 uc/arb SNS Experimental Facilities 29 Oak Ridge

The ING Project: Machine Specifications • Proton linac • Length: • • – Alvarez section – 110 m – Waveguide section – 1430 m Total RF power – 90 MW Energy – 1 Ge. V Current – 65 m. A (CW) Proton beam power – 65 MW X 0000910/arb 2000 -05258 uc/arb SNS Experimental Facilities 30 Oak Ridge

Perspective View of ING (artist’s conception) X 0000910/arb 2000 -05259 uc/arb SNS Experimental Facilities 31 Oak Ridge

The ING Project: Target System • • Flowing Pb-Bi eutectic, 20 cm ø, 60 cm long Vertical (downward) incident proton beam Beryllium “Multiplier” thickness 20 cm D 2 O moderator – 100 cm radius Global neutron production rate 1019 n/sec Max thermal neutron flux 1016 n. Th/cm 2 -sec Beam tubes, 5 tangential (10 cm ø), one radial (10 cm ø), one through-tube (20 cm ø) X 0000910/arb 2000 -05260 uc/arb SNS Experimental Facilities 32 Oak Ridge

Cutaway View of the Target Building X 0000910/arb 2000 -05261 uc/arb SNS Experimental Facilities 33 Oak Ridge

Lead-bismuth Eutectic Flow in Target Zone X 0000910/arb 2000 -05262 uc/arb SNS Experimental Facilities 34 Oak Ridge

Intense Neutron Generator • 1952 W. B. Lewis promotes spallation and accelerators for • • neutron production 1960 s at CRNL – 65 m. A CW protons to 1 Ge. V – Accelerator development – Pb-Bi loops – Experimental facilities and design – Cockcroft-Walton limitation – 35 m. A CW at 750 ke. V Led to Accelerator Breeder program in 1970 s – ZEBRA in 1980 s X 0000910/arb 2000 -05263 uc/arb SNS Experimental Facilities 35 Oak Ridge

Measured Neutron Yield vs. Proton Energy for Various Targets From Fraser et al. , measurements at Brookhaven Cosmotron SNS Experimental Facilities 36 X 0000910/arb 2000 -05264 uc/arb Oak Ridge

Pulsed Spallation Neutron Sources (primary source pulse widths of all are less than 0. 5 µsec) X 0000910/arb 2000 -05277 uc/arb SNS Experimental Facilities 37 Oak Ridge

Pulsed Spallation Neutron Source Construction, Proposals and Studies X 0000910/arb 2000 -05278 uc/arb SNS Experimental Facilities 38 Oak Ridge

Anatomy of a Pulsed Spallation Source X 0000910/arb 97 -3792 B uc/djr SNS Experimental Facilities 39 Oak Ridge

The Spallation Neutron Source • • • The SNS will begin operation in 2006 At 2 MW it will be ~12 x ISIS with a time averaged flux ~NIST The peak thermal neutron flux will be ~125 x NIST SNS will be the world’s leading facility for neutron scattering It will be a short drive from HFIR, a reactor source with a flux comparable to the ILL (~3 x NIST) X 0000910/arb SNS Experimental Facilities 40 Oak Ridge

Summary Parameters for the SNS • • • • Proton beam power on target Average proton beam current on target Pulse repetition rate Peak linac H- current Chopper beam-on duty factor Linac length, with 5 empty cryomodule slots DTL output energy Number of DTL 402. 5 -MHz 2. 5 -MW klystrons CCL output energy Number of CCL 805 -MHz 2. 5 -MW klystrons SRF linac output beam energy Number of SRF cavities Number of linac 805 -MHz 0. 5 -MW klystrons 2. 0 MW 2. 0 m. A 60 Hz 52 m. A 68 % 331 m 87 Me. V 7 185 Me. V 8 ~1. 0 Ge. V 97 97 X 0000910/arb 2000 P-03544/jhb SNS Experimental Facilities 41 Oak Ridge

Summary Parameters for the SNS (cont. ) • • • • Linac beam duty factor HEBT length Accumulator ring circumference Ring orbit rotation time Number of injected turns Ring fill time Ring beam extraction gap RTBT length Protons per pulse on target Proton pulse width on target Target material Number of ambient/composite/cold mod. Number of neutron beam shutters Initial number of instruments 6. 0 % 170 m 248. 0 m 945 ns 1060 1. 0 ms 250 ns 151 m 2. 08 E+14 695 ns Hg 1/1/2 18 10 X 0000910/arb 2000 P-03545/jhb SNS Experimental Facilities 42 Oak Ridge

Function – – Create 65 -m. A H- ion beam Accelerate beam to 2. 5 Me. V Chop beam into mini-pulses Match 52 -m. A beam into Drift-Tube Linac Ion Source/LEBT RFQ LEBT/MEBT RFQ LEBT Ion Source X 0000910/arb 2000 P-03547/jhb SNS Experimental Facilities 43 Oak Ridge

SNS High Beta Cryomodule X 0000910/arb SNS Experimental Facilities 44 Oak Ridge

Ring Lattice X 0000910/arb 2000 P-03550/jhb SNS Experimental Facilities 45 Oak Ridge

SNS High Power Target Station X 0000910/arb 2000 -03440/arb SNS Experimental Facilities 46 Oak Ridge

Target Systems Summary • 2 -MW mercury target, • • shielding, remote handling, neutron beam transport 3 beam dumps Associated R&D: target test facility, materials compatibility, thermal shock TEC 85. 9 M$ R&D 17. 3 M$ X 0000910/arb 2000 -03443/arb SNS Experimental Facilities 47 Oak Ridge

Target Building Scope of Target Building • Multistory building 202 feet wide by 325 feet long • Instrument floor houses neutron instruments, instrument/target shops • • • to support experimenters and target mock up activities RTBT shielded area brings beam to target Target Shield Stack and Hot Cell are bulk of category 2 nuclear facility housing Target and Target Maintenance Facilities Basement area includes services for the entire building, a portion is included in the nuclear facility The high bay area houses the cryogenic system for the moderators and allows access for maintenance of target system components The west yard contain service areas bringing in building utilities including helium and nitrogen X 0000910/arb SNS Experimental Facilities 48 Oak Ridge

Target Building - Current Layout X 0000910/arb SNS Experimental Facilities 49 Oak Ridge

Target Building - Current X 0000910/arb SNS Experimental Facilities 50 Oak Ridge

Instrument Planning • A full, 24 instrument, experimental hall layout has been developed to • provide constraints on target/conventional interfaces and facilitate instrument planning Includes instrument under study plus realistic “placeholders” X 0000910/arb 2000 -03453/arb SNS Experimental Facilities 51 Oak Ridge

Long Wavelength Target Station • The Spallation Neutron Source (SNS) is designed from the outset to allow operation with two target stations X 0000910/arb 2000 -03457/arb SNS Experimental Facilities 52 Oak Ridge